1. Insect Infestation
It has been estimated that about ten percent of the world's grain production is lost during storage because of insect infestation. Not only do the insects consume the grain, but they also generate dust and contaminate the grain with insect fragments, feces, webbing, metabolic products, and a variety of microflora. Because of the size of the losses, there has been a tremendous amount of research on the control of insects. While methods of control studied have included improved sanitation and physical separation methods, probably the most common method of control is the application of an insect control agent on or near the grain. Insect control agents act in many different ways; for example, some kill the insect upon physical contact or ingestion, some disrupt the reproductive cycle, and some merely repel the insects. Insect control agents include various biological agents, such as pheromones, and chemical agents, such as insecticides. At this time, the chemical agents are more frequently used than the biological agents.
Chemical insecticides are widely recognized as effective at controlling insects. Such insecticides can be applied as dusts, wettable powders, aerosols, solutions, and emulsions. Although effective, chemical insecticides suffer serious drawbacks because of toxic residues they leave on the grain and the serious dangers they pose to workers handling them and/or the treated grain. Accordingly, the use of chemical insecticides on food materials is strictly regulated. Another drawback is that the chemical insecticides are generally quite expensive and, since many of these insecticides and/or their carriers are derived from petroleum-based feedstocks, their costs have rapidly increased over the past decade. Last but not least of the drawbacks is the phenomenon of genetic resistance which decreases the effectivess of a given insecticide over time.
Therefore, it is not surprising that considerable attention has been focused on the use of substances which control insects when applied to the grain and which are inexpensive, non-toxic, and less prone to the effects of genetic resistance. One such substance is white mineral oil, also called petrolatum, which is a petroleum fraction boiling in the range of about 330.degree. to 390.degree. C. and having a specific gravity at 25.degree. C. of about 0.82 to 0.90. Although white mineral oil is believed to be non-toxic, it is not digestible and therefore adds no nutritional value to the treated grain. And, since it is derived from petroleum, the cost of white mineral oil has increased substantially over the past decade. Another substance which is reported to be effective at controlling insects is vegetable oil. Although vegetable oil has been used since ancient times to protect grain from insect infestation, this use has become the subject of renewed interest. For example, S. R. Singh et al. have reported that cowpea seeds are protected against infestation by the cowpea weevil, Callosobruchus Maculatus (F), when treated with groundnut oil at 5 ml/kg or with castor, coconut, or palm kernel oils at 8 ml/kg. S. R. Singh et al., "Groundnut Oil Treatment For The Control of Callosobruchus Maculatus (F) During Cowpea Storage", J. Stored Prod. Res. (Vol. 14, pp. 77-80, 1978). This study indicated that the method of control was primarily by progeny mortality rather than reduced oviposition (egg-laying) or adult mortality. It was theorized that the action of the oil within the egg may be due to both chemical toxicity and the physical properties of the oil.
In another study, A. V. Schoonhoven tested a number of different vegetable oils for their efficacy in protecting bean seeds, Phaseolus vulganis (L.) from attack by the bruchid, Zabrotes subfasciatus. A. V. Schoonhoven, "Use of Vegetable Oils to Protect Stored Beans from Bruchid Attack", J. Econ. Entomol. (Vol. 71, pp. 254-256, 1978). The oils tested included African palm, crude cottonseed, purified cottonseed, maize, crude soybean, purified soybean, crude coconut palm, and purified coconut palm. Schoonhoven noted that progeny emergence was reduced significantly by the addition of only 1 ml oil/kg of beans and that the addition of 5 ml oil/kg of beans caused 100% adult mortality two days after infestation and completely eliminated oviposition. Schoonhoven also stated that crude oils provided significantly better protection than purified oils and that the level of control of different oils varied significantly. A subsequent article co-authored by Schoonhoven reported that the triglyceride fraction of vegetable oils was the active component in insect control. J. Hill and A. V. Schoonhoven, "Effectiveness of Vegetable Oil Fractions in Controlling the Mexican Bean Weevil on Stored Beans" , J. Econ. Entomol. (Vol. 74, pp. 478-479, 1981).
Another report concerns the effect of vegetable oils on protecting wheat from infestation by the granary weevil, Sitophilus granarius (L). Y. T. Qi and W. E. Burkholer, "Protection of Stored Wheat From the Granary Weevil by Vegetable Oils", J. Econ. Entol. (Vol. 74, No. 5, pp. 502-505, 1980). The vegetable oils tested were soybean, maize, peanut, and cottonseed oils. The authors do not state whether the oils were crude or refined. In testing the effect of oil-treated wheat seeds on progeny emergence, Qi and Burkholder noted that treatment at a 1 ml/kg dosage had little effect, but that treatment at a 5 ml/kg dosage significantly reduced progeny emergence for all the oils tested. Similarly, Qi and Burkholder noted that the 5 ml/kg dosage had little effect on mortality of adult weevils, but that significant mortality was produced at the 10 ml/kg level. Soybean oil was said to produce the highest degree of mortality, followed in order by maize, peanut, and cottonseed oils.
As the above reports indicate, the application of vegetable oils in sufficient amounts is believed to control insect infestation. It is also believed that the action of vegetable oils on insects is less prone to the effects of genetic resistance. And, of course, it is well known that vegetable oils are readily available, relatively inexpensive, and non-toxic. The major drawback to the use of vegetable oils is that they are, to a greater or lesser degree, prone to hydrolytic and oxidative rancidity. Therefore, the use of vegetable oil on grain can result in the grain developing an unpleasant odor and/or taste over time. Accordingly, a need still exists for a substance which controls insects and possesses the many other advantages of the vegetable oils, but is less prone to rancidity. Ideally, the substance would also be even more effective at controlling insects so that it could be applied in smaller amounts.
While there is nothing to suggest that phosphatides are effective at controlling insects, the use of lecithin, which contains a high concentration of phosphatides, in insecticide formulations is known. For example, in 40 C.F.R. Section 180.1001 (1982), the use of lecithin meeting Food Chemicals Codex specification as an emulsifier in pesticide formulations is exempted from the requirement of a tolerance. Cardarelli, U.S. Pat. No. 4,237,113, also discloses the use of lecithin as a component in an insecticide formulation. Cardarelli teaches that a slow release insecticide is prepared by mixing together a polyolefin, a halogenated organotin, and an agent which induces and enhances porosity within the polyolefin, and then coalescing the mixture by heating and before partitioning for use. Cardarelli states that the porosity-inducing agent can be insert, but it is preferable to employ an agent which is also an attractant for various insects. The preferred attractant-porosigen agents are soy oil and lecithin.
2. Grain Dust
It is well known that grain dust is an irritant when inhaled, a source of grain loss, a problem to machinery, and a nuisance from a cleanliness standpoint. However, the greatest problem with grain dust is that it is an oxidizable material which, under certain conditions, can ignite and burn. The combustion of the dust is accompanied by an increase in pressure resulting from the conversion of solid reactants to gaseous products. The increase in pressure can occur so quickly that equalization does not occur, resulting in the production of a shock wave. This shock wave can, in turn, produce a violent explosion. Grain dust explosions at grain handling locations have been recorded for hundreds of years. During the two months of December, 1977, and January, 1978 alone, there were seven grain dust explosions in the United States of America resulting in the loss of 62 lives, 55 injuries, and a direct property loss of millions of dollars. It is considered likely that the Occupational Safety and Health Administration will soon, for the first time, prepare grain elevator safety standards limiting accumulations of grain dust.
Mixtures of grain dust and oxygen do not spontaneously ignite; an ignition source of sufficient temperature and energy must be present. However, such sources are often present in grain handling facilites. For example, studies have indicated that probable ignition sources in past explosions include welding, cutting, electrical failures, static electricity, friction sparks, etc. It is also well documented that the ignition and combustion of grain dust is affected by a number of factors, for example, density of the dust; particle size, chemical composition and moisture content of the dust particles; and chemical composition and moisture content of the gas.
There are many precautions taken to reduce the possibility and risks of a grain dust explosion. These are principally mechanical: to reduce sources of ignition and to reduce dust concentration with precipitators, filters and the like. All entail high capital costs and energy expenditures.
A different approach to reducing dust levels is to treat the grain with a dust suppressant. The ideal dust suppressant would have no deleterious effect on the grain and would remain effective at suppressing grain dust for long periods of time so that only one application would be necessary. One grain dust suppressant which has been used with some success is water. See, for example, F. S. Lai et al., "Control of Grain Dust With A Water Spray", Cereal Foods World (Vol. 27, No. 3, pp. 105-107, 1982). While water appears to be reasonably effective and is, of course, inexpensive, it is not the ideal suppressant. First of all, water evaporates and may have to be reapplied at each point the grain is handled. Secondly, the addition of water to grain increases the risk of fungus and mold formation and other decay.
Another study has indicated that soybean oil and mineral oil are both effective at suppressing grain dust. F. S. Lai et al., "Reducing Grain Dust With Oil Additives", Transactions of the ASAE (Vol. 24, No. 6, pp. 1626-1631, 1981). The researchers found that the addition of 0.04 weight percent soybean oil to Number 1 yellow dent corn reduced its dustiness to 5.4 percent of the control. Because conventionally refined soybean oil is subject to hydrolytic and oxidative rancidity, the researchers used a specially refined soybean oil having an AOM stability of 350 hours to a 100 peroxide value. The addition of mineral oil to the corn caused an even greater reduction in dustiness. The researchers further discovered that the duration of dust suppression was longer for mineral oil than for soybean oil. See also Moen, U.S. Pat. No. 2,585,026 which discloses the use of mineral oil-water emulsions for controlling grain dust.
Barham, Jr., U.S. Pat. No. 4,208,433, discloses the use of vegetable and mineral oils to reduce grain dust. Barham suggests that when the ratio of dust to oil is properly balanced, a synergistic effect results and the oil and the dust are completely incorporated into the grain. Barham states, at col. 7, lines 34-35, that the ratio of dust to oil is usually from 1:1 to 6:1, with 4.5:1 being a common ratio. At col. 20, lines 35-39, Barham states, in effect, that wheat often contains about 0.06 to 0.2 percent dust based on grain weight. Accordingly, to achieve the synergistic effect, it would be expected that the oil be present in an amount of about 0.01 to 0.2 weight percent of the grain. Barham states that "oils, fats, and greases of all sources are applicable" and that the choice for commercial application "will center around the relative costs and intended usage."
Notwithstanding the above-described teaching, a need still exists for a dust suppressant which is inexpensive, more stable, more effective, and which can impart other favorable properties to the grain.